In the art it is desirable to produce elastomeric compounds exhibiting reduced hysteresis. Such elastomers, when compounded to form articles such as tires, power belts and the like, will show an increase in rebound, a decrease in rolling resistance and will have less heat build-up when mechanical stresses are applied.
Previous attempts at preparing reduced hysteresis products have included high temperature mixing of the filler-rubber mixtures in the presence of selectively-reactive promoters to promote compounding material reinforcement; surface oxidation of the compounding materials; chemical modifications to the terminal end of polymers using tetramethyldiaminobenzophenone (Michler's ketone), tin coupling agents and the like and surface grafting thereon.
It has also been recognized that carbon black, employed as a reinforcing filler in rubber compounds, should be well dispersed throughout the rubber in order to improve various physical properties. One example of the recognition is provided in published European Pat. Appln. EP 0 316 255 A2 which discloses a process for end capping polydienes by reacting a metal terminated polydiene with a capping agent such as a halogenated nitrile, a heterocyclic aromatic nitrogen containing compound or an alkyl benzoate. Additionally, the application discloses that both ends of the polydiene chains can be capped with polar groups by utilizing functionalized initiators, such as lithium amides.
Organolithium polymerization initiators are also known in the art. U.S. Pat. No. 3,439,049 discloses an organolithium initiator prepared from a halophenol in a hydrocarbon medium.
U.S. Pat. No. 4,015,061 is directed toward amino-functional initiators which polymerize diene monomers to form mono- or di-primary aryl amine-terminated diene polymers upon acid hydrolysis.
U.S. Pat. No. 4,935,471 discloses dicapped polymers obtained using certain N--Li initiators, including piperidinyl and pyrrolidinyl oligoalkylamino lithiums. It has been found that piperidine-based initiators result in polymers having inferior interaction with compounding materials such as carbon black, and hence, result in little if any reduction in the hysteresis characteristics of the polymers. It has further been found that pyrrolidine-based polymers have a strong and offensive odor, making their use commercially undesirable.
The present invention provides novel initiators for anionic polymerization which become incorporated into the polymer chain providing a functional group which greatly improves the dispersability of carbon black throughout the elastomeric composition during compounding. As will be described hereinbelow, these initiators are a product of the reaction between the diene adducts of cyclic secondary amines and an organolithitun compound.